Japanese Oatent No. 63/16157 describes a prior art example of a control apparatus for a washing machine, which is provided with a transmission factor detection apparatus for detecting the degree of dirtiness of the washing liquid within the tub of the washing machine. That control apparatus consists of the transmission factor detection apparatus, which detects the optical transmission factor of the washing liquid within the tub, and a judgement section for detecting changes in that optical transmission factor, as indicated by an output signal from the transmission factor detection apparatus, while a washing operation is in progress. When the optical transmission factor of the washing liquid is found to have ceased to change, the judgement section judges that as indicating that the washing operation is to be ended. When the judgement section thus judges that the washing oepration is to be ended, then after halting the washing operation, the discharge valve of the washing machine is opened, and the washing liquid is discharged through a discharge pipe. During that discharge process, the optical transmission factor of the washing liquid that is flowing through the discharge pipe is judged. Since foam which is produced in the washing operation will be mixed into the washing liquid as that liquid is being discharged, the optical transmission factor as detected by the transmission factor detection apparatus will be reduced due to dispersion of the sensing light within the foam in the discharged washing liquid. The greater the amount of foam in the washing liquid, the greater will be the degree of dispersion of the light, and hence the greater will be the amount of reduction of the optical transmission factor that is detected by the transmission factor detection apparatus. Thus be detecting the amount of lowering of optical transmission factor which occurs during the washing liquid discharge operation, it is possible to detect the amount of foam in the washing liquid, and hence to detect the proportion of cleanser that remains in the washing liquid, so that the degree of washing power that remains in the washing liquid can be detected. The amount of lowering of the optical transmission factor during the washing liquid discharge operation is compared with a judgement amount, and if the amount of lowering is not to be sufficiently small, then a warning indication is given that the washing process has been insufficient.
With such a control apparatus for a washing machine, since the optical transmission factor is detected by the transmission factor detection apparatus during a washing operation, and the point in time at which changes in the optical transmission factor are found to have ended is taken as the point at which the washing operation is to be terminated, the problem arises that the degree of washing that has been performed may be insufficient in some cases. For example if the type of dirt that is to be removed is mud, then the changes in optical transmission factor will end within a short time, i.e. the mud will dissolve in the washing liquid within a short time, so that the changes in optical transmission factor will correspondingly be ended within a short time. However at that point in time, there may still remain some types of dirt such as mud or grease etc., adhering to the material being washed, so that the degree of washing will have been insufficient.
Moreover with such an apparatus, if it is judged by the apparatus after the washing operation has ended that the degree of washing was not sufficient, then a warning indication is issued to inform the user that the washing operation must be repeated. In such a case, the user must then again repeat the washing operation, which is inconvenient and is a problem of that apparatus.